Add an Internal Application File LoggerPolicy simple example

Former-commit-id: ac7bfd25c1302f9c304c888c28804a6f5a00328c

_examples/README.md

@@ -12,6 +12,7 @@ It doesn't contains "best ways" neither explains all its features. It's just a s
     * [Hello World](beginner/hello-world/main.go)
     * [Routes (using httprouter)](beginner/routes-using-httprouter/main.go)
     * [Routes (using gorillamux)](beginner/routes-using-gorillamux/main.go)
+    * [Internal Application File Logger](beginner/file-logger/main.go)
     * [Write JSON](beginner/write-json/main.go)
     * [Read JSON](beginner/read-json/main.go)
     * [Read Form](beginner/read-form/main.go)

_examples/beginner/file-logger/main.go

@@ -0,0 +1,63 @@
+package main
+
+import (
+	"log"
+	"os"
+
+	"gopkg.in/kataras/iris.v6"
+	"gopkg.in/kataras/iris.v6/adaptors/httprouter"
+)
+
+var myLogFile *os.File
+
+func init() {
+	// open an output file
+	f, err := os.Create("logs.txt")
+	if err != nil {
+		panic(err)
+	}
+	myLogFile = f
+}
+
+func myFileLogger() iris.LoggerPolicy {
+
+	// you can use a *File or an io.Writer,
+	// we want to log with timestamps so we use the log.New.
+	myLogger := log.New(myLogFile, "", log.LstdFlags)
+
+	// the logger is just a func,
+	// will be used in runtime
+	return func(mode iris.LogMode, message string) {
+		// optionally, check for production or development log message mode
+		// two modes: iris.ProdMode and iris.DevMode
+		if mode == iris.ProdMode {
+			// log only production-mode log messages
+			myLogger.Println(message)
+		}
+	}
+}
+
+func main() {
+	// close the log file on exit application
+	// when panic or iris exited by interupt event or manually by Shutdown.
+	defer func() {
+		if err := myLogFile.Close(); err != nil {
+			panic(err)
+		}
+	}()
+
+	app := iris.New()
+	app.Adapt(myFileLogger())
+	app.Adapt(httprouter.New())
+
+	app.Get("/", func(ctx *iris.Context) {
+		// for the sake of simplicity, in order see the logs at the ./logs.txt:
+		app.Log(iris.ProdMode, "You have requested: http://localhost/8080"+ctx.Path())
+
+		ctx.Writef("hello")
+	})
+
+	// open http://localhost:8080
+	// and watch the ./logs.txt file
+	app.Listen(":8080")
+}